Method of operating a combustible mixture generator of an internal combustion engine and apparatus for carrying out the method

ABSTRACT

In order to produce a transition mixture enrichment during acceleration of an internal combustion engine, a carburettor or other mixture generator 1 of the engine with a mixing chamber 2, a main throttle 4 and a choke valve 5, has the choke valve 5 operated by a quick-acting electric drive 6, for example a two-coil rotary setter, which is controlled by a microprocessor 8. The microprocessor is fed with signals which sense the opening of the main throttle 4 and preferably also other engine operating parameters such as temperature and speed. When the main throttle 4 is opened to accelerate the engine, the microprocessor 8 causes the electric drive 6 to close the choke valve 5 abruptly and temporarily. The extent of closure of the choke valve 5 is dependent upon the extent of the throttle opening and on the other operating parameters to give the required mixture enrichment. This arrangement avoids the necessity to provide an accelerator pump.

This invention relates to a method of and apparatus for operating acombustible mixture generator of an internal combustion engine toproduce a transition mixture enrichment during acceleration of theengine, the mixture generator comprising a mixing chamber, a mainthrottle downstream of the chamber and a choke valve upstream of thechamber, an electric drive operating the choke valve, and a controldevice which senses at least one operating parameter of the engine andcontrols the electric drive to move the choke valve into positions forcold starting, running-up and hot-running mixture enrichment.

The choke valve which is in the form of a flap of an automatic choke ofa fixed venturi carburettor is usually acted upon by a bi-metal springheated in dependence upon the engine temperature and by a diaphragmacted upon by the reduced pressure in the engine inlet to set itsangular position in order to achieve satisfactory cold-starting,running-up and hot-running enrichment of the mixture. According toGerman Offenlegungsschriften Nos. 25 11 288, 25 16 477, 25 25 594 and 2525 595, in order to carry out these enrichment operations, the bi-metalspring and the diaphragm controlled by the reduced pressure aredispensed with and instead the choke valve flap is coupled to a steppingmotor through a spiral spring which is not temperature sensitive. Themotor is controlled depending on operating parameters, particularly theengine temperature, to rotate the choke-valve flap through the springconnection. In all these existing arrangements, moreover, the angularadjustment of the main throttle which is another flap is controlleddepending on temperature, usually through a stepped cone drive. This hasthe important disadvantage that the accelerator pedal has to be pressedfully down and be released before starting the engine. Further, in allexisting arrangements of this kind, a separate accelerator pump isprovided and is coupled to the main throttle flap. This ensures thatadditional fuel is injected into the mixing chamber on an acceleratingactuation of the main throttle flap. Thus the existing arrangements arerelatively complicated in construction, comparatively expensive,difficult to operate and liable to breakdown, for example because of therisk of the formation of gas bubbles in the accelerator pump.

It is an object of the present invention to provide a method and anapparatus as initially described which avoid the disadvantages outlined,so that all the necessary mixture enrichment operations, particularlythe transition enrichment, can be carried out in a very reliable andsimple manner with a single final control element.

To this end, according to one aspect of this invention, a method asinitially described is characterised by holding the choke valve open insteady operation of the engine and temporarily abruptly at least partlyclosing the choke valve by means of the electric drive upon operation ofthe main throttle to accelerate the engine. Thus, the electric drive notonly effects the cold-starting, running-up and hot-running enrichment ofthe mixture as is known, but now in addition also effects the transitionenrichment by the abrupt temporary closing of the choke valve memberupon acceleration taking place. As a result of the rapid movement of thechoke valve and the rapid pressure reduction which occurs as a result inthe mixing chamber down almost to the engine inlet pressure, the effectis achieved that the main fuel supply system to the chamber comes intoaction very quickly and delivers larger amounts of fuel. As a result ofthis, in synchronism with each acceleration, the additional amount offuel needed for the compensation of flat spots is supplied practicallywithout delay. The method in accordance with the invention can be usedwith fixed venturi carburettors and with constant-pressure carburettors,particularly when an appropriate choke valve is connected into the airflow path of the latter.

In the method in accordance with the invention, the magnitude andduration of the closing of the choke valve during acceleration ispreferably made dependent on measured operating parameters of theengine, for example in such a manner that the magnitude and the durationof the closing are made smaller, the greater the degree of opening ofthe main throttle that exists before the acceleration takes place, thelower the rate and degree of acceleration, that is throttle opening, thehigher the engine temperature and the higher the engine speed.Furthermore, the closing of the choke valve is preferably effected whenthe rate of opening of the main throttle exceeds a predeterminedthreshold value. Below this threshold value, that is to say withrelatively slow opening adjustments of the main throttle, there is notsufficient acceleration to make any closing of the choke valvenecessary. Above the threshold value, an optimum control behaviour withregard to exhaust gas composition, running behaviour and fuelconsumption of the engine is achieved by controlling the magnitude andduration of the closing of the choke valve in dependence on theoperating parameters. In order to avoid excessive mixture enrichment onrepeated actuation of the main throttle, it is further desirable to takeinto consideration the time between two accelerating operations indetermining a new magnitude and duration of the closing of the chokevalve or the new increased amount of fuel. After expiration of a periodof time, a gradual opening operaton may appropriately be carried out,preferably linearly in time.

According to another aspect of the invention, apparatus for carrying outthe method in accordance with the invention comprises a combustiblemixture generator for an internal combustion engine, the mixturegenerator comprising a mixing chamber, a main throttle downstream of thechamber and a choke valve upstream of the chamber, an electric driveoperating the choke valve, and a control device which senses at leastone operating parameter of the engine and controls the electric drive tomove the choke valve into position for cold starting, running-up andhot-running mixture enrichment, wherein the electric drive is in theform of a quick-acting drive and is torsionally rigidly connected to thechoke valve, and the control device is connected, at its input side, toa sensor which senses the opening of the main throttle and produces asignal which operates the drive to close the choke valve abruptly andtemporarily when opening of the main throttle is sensed.

When the main throttle is in the form of a flap, the sensor is in theform of an angular-position sensor. This can be inductive or opticallycoded angle indicator or, in a simple example, a potentiometer, a tap ofwhich is in mechanical driving connection with the main throttle flap.The control device preferably includes a circuit which is connected tothe condition sensor and differentiates with respect to time the angularposition of the main throttle to provide a signal indicating the rate ofopening of the throttle.

As a result of the torsionally rigid driving connection of the electricdrive to the choke valve and the sensor coupled to the main throttle,the apparatus in accordance with the invention makes possible an abruptclosing of the choke valve when acceleration takes place so that amechanical accelerator pump is no longer necessary. In addition, thetransition mixture enrichment is initiated in a very reliable manner,without delay, because the main fuel supply system to the mixturegenerator is acted upon by almost the full suction pressure in theengine inlet owing to the abrupt closing of the choke valve asacceleration takes place. It is possible to detect the opening speed ofthe main throttle directly in order to etect the acceleration, but thispresupposes separate sensors for detecting the opening and the speed ofopening. Calculation of the speed of opening by differentiation withrespect to time of the angular position of the main throttle is simpler.This differentiation can be effected by a microprocessor which thenforms the control device.

The control device of the apparatus which is actuated in dependence onthe angular position or the degree of opening of the main throttle andpreferably also opening speed is preferably further connected to anengine speed sensor and at least one engine temperature sensor. A sensorwhich detects the temperature of the wall of an engine inlet manifold ispreferably also provided in order to achieve a particularly favourablemixture enrichment relationship. With certain forms of construction,this last-mentioned sensor may be disposed in the vicinity of an inletmanifold cooling water passage so that only a single temperature sensoris necessary and this senses a temperature which is related to both thecooling water temperature and the manifold temperature.

For a simple, reliable and economical realisation of the controlfunctions, a microprocessor which converts the various operatingparameters fed to its input side into control signals for the electricdrive at its output side in dependence upon engine operating performancedata stored in the microprocessor is preferred as a control device. Suchan electronic device makes it possible to make a very rapid, accurateand absolutely reliable calculation of control signals depending oninput operating parameters and stored operating performance data withthe minimum use of space and minimum cost.

A transition mixture enrichment which is brought about without delaywhen acceleration takes place is assured as the electric drive of thechoke valve works very quickly when actuated and reaches its desiredposition abruptly. If the choke valve is constructed in the form of apivotally mounted choke valve flap, it is extremely advantageous toconstruct the electric drive in the form of a two-coil rotary setterwhich operates in the manner of a two-phase synchronous notor withwindings mutually offset by an angle of 90°, the coils of the setterbeing controllable independently of one another by direct currents, anda permanent-magnet rotor being moved by the magnetic field produced bythe coils. The direction of the magnetic field of the two-coil rotarysetter energised by direct current results from the ratio in magnitudeof the direct currents supplied to the coils and the low-inertiapermanent-magnet rotor can adjust itself without delay and veryprecisely to the particular direction of the magnetic field. In thiscase no measuring and restoring of the rotor angle setting is necessary,as would be the necessary, for example, if a direct-current motor or arotary magnet were used.

Instead of detecting certain other operating parameters, it is alsopossible to provide an air-volume meter in the air flow path of themixture generator and to connect the output of the meter to the input ofthe control device. This embodiment is logical if air-volume meterssuitable for this purpose can be made at reasonable cost.

An example of a method and of apparatus in accordance with the inventionwill now be described with reference to the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic general view of the apparatus;

FIGS. 1a, 1b, 1c and 1d are schematic illustrations of different controlembodiments in accordance with the present invention;

FIG. 2 shows graphs of cold-running, running-up and hot-running mixtureenrichment against time; and,

FIG. 3 shows graphs of transition mixture enrichment against time duringacceleration.

In FIG. 1, a combustible mixture generator 1 is illustrated in the formof a fixed venturi carburettor with a mixing chamber 2, in which thereis a preliminary fuel atomiser 3. Downstream of the mixing chamber 2 isa main throttle 4 in the form of a pivotable main throttle flap, andupstream of the mixing chamber 2 is a choke valve 5 which, in thisexample, is constructed in the form of an eccentrically mounted,pivotable choke valve flap. The choke valve 5 is connected, through atorsionally rigid driving connection 7, to the output of an electricdrive 6 in the form of a quick-acting two-coil rotary setter. At itsinput side, the rotary setter 6 is connected, through an electricalthree-conductor connection 9, to the control output of an electroniccontrol device 8 which, in the present example, is a microprocessor.Stored in the memory of the microprocessor are the operating performancegraphs necessary for controlling the cold-starting, running-up,hot-running and transition mixture enrichment, by means of which controlsignals for the electric drive 6 are calculated in dependence on theoperating parameters fed into the microprocessor.

A position sensor 10 which, in the present example, is in the form of apotentiometer 11, has an adjustable tap 12 which has a mechanicaldriving connection 13 to the main throttle 4. The sensor 10 detects theangular position or the instantaneous degree of opening of the mainthrottle 4. The potentiometer 11 is electrically fed, through supplylines 14, from the control device 8, and its tap 12 is adjusted insynchronism with the angular position α₂ of the main throttle member 4.An electrical signal corresponding to the angular position α₂ is takenoff at the tap 12 and supplied via a tap line 15 to the control device8. This contains a program section with which the angular position α₂ ofthe main throttle member 4 is differentiated with respect to time so asto produce an adjusting speed signal dα₂ /dt as an operating parameter.This speed signal is preferably supplied, in the control device 8, to aprogram section working as a threshold-value detector which onlyproduces a signal indicating that there is an accelerating operationwhen the throttle is being opened at a speed above a predeterminedminimum. Only in this case is a control operation of the electric motordrive 6 initiated which influences the degree of opening or the angularposition α₁ of the choke valve flap 5. In another embodiment aninductive angle indicator 30 can be used in place of the potentiometer11, note FIG. 1a. The inductive angle indicator is connected to the mainthrottle 4 by the mechanical driving connection 13 and to the controldevice 8 by a line 34. In a further embodiment the potentiometer 11 isreplaced by an optical angle indicator 40 which is connected to the mainthrottle valve 4 by the mechanical driving connection 13 and to thecontrol device 8 by a line 44.

The control device 8 is also connected, at its input side, to an enginespeed sensor 16, which may as a simple example be a detector whichdetects the ignition pulse from an ignition system of the engine. Anengine-temperature sensor 17, which, for example, detects thetemperature of the engine cooling water, is preferably constructed inthe form of a resistor with a negative temperature coefficient and isconnected to the input side of the control device 8. In the presentexample, a sensor 18 for sensing the temperature of the wall of theinlet manifold of the engine is further provided. This is likewiseconstructed in the form of a negative temperature coefficient resistorand is connected to the input of the control device 8. Both sensors maybe replaced by a single temperature sensor if the temperature of theinlet manifold wall is sensed in the vicinity of the place where thecooling water is circulated.

In the upper part of FIG. 2, the speed n of the engine which occursduring starting is shown plotted against time. During the starting ofthe engine, a starter speed n_(A) results and at the instant t₁ a speedthreshold n_(S) is reached. The time up to the instant t₁ can be calledthe starting time. After that, the speed n increases ultimately up tothe idling speed n₀, and the time between t₁ and t₂ can be called therunning-up time. Then follows the hot-running time within which theidling speed n₀ remains substantially constant. In the lower part ofFIG. 2, the degree of opening or the angular position α₁ of the chokevalve 5 is plotted against time. During the starting time up to t₁ thechoke valve 5 is kept closed. In the running-up time, opening of thechoke valve 5 is at first delayed to obtain a somewhat richer mixtureand ensure reliable running-up. After that, in the latter part of therunning-up time (between t₁ and t₂) in the present example, the chokevalve 5 is opened in two different operations, which are linear in time,at first rapidly and then more slowly up to a certain intermediateposition which depends on the temperature of the cooling water. Duringthe hot-running time following t₂, the position of the choke valve isdependent upon the rising temperature of the cooling water and on theconsequently necessary decreasing mixture enrichment. Thus, the chokevalve 5 is gradually opened completely depending on the temperature ofthe cooling water.

The cold-starting, running-up and hot-running mixture enrichmentoperations illustrated in FIG. 2 are known per se and are carried outindependently of acceleration enrichment.

When, as shown in the upper part of FIG. 3, the main throttle 4 isopened sufficiently quickly from a first angular position α_(2A) to asecond angular position α_(2B), that is to say when the speed of openingof the main throttle 4 exceeds a certain threshold value, as shown inthe lower part of FIG. 3, the open choke valve 5 is closed again,without delay, at the instant t₃ when acceleration starts, into anangular position α_(1B) which is set to provide the required amount oftransition enrichment. This new angular position, which is reached asabruptly as possible, is retained during a period between t₃ and t₄.Then follows a gradual opening of the choke valve 5, in the presentexample linearly in time, until the full degree of opening is againreached at the instant t₅. As already mentioned, the magnitude of theangle α_(1B) and the period of time between t₃ and t₄ are made dependenton various operating parameters fed into the control device 8,particularly on the angular position α_(2A) of the main throttle 4before acceleration starts, on the speed of opening dα_(2A) /dt duringthe acceleration, on the engine temperature, optionally on thetemperature of the wall of the inlet manifold, on the engine speed andoptionally also on the time which has elapsed from the previous to thenew accelerating throttle actuation. The opening operation of the chokevalve 5, linearly in time, between the times t₄ and t₅ is only given byway of example and can also be carried out in other ways.

When an accelerating operaion is recognised by the control device 8 onexceeding of the predetermined threshold value of the opening speed ofthe main throttle 4, direct current control signals for the electricdrive 6 are produced by the microprocessor in dependence on theoperating parameters fed into the device and on performance data storedin the device. The drive 6, which is constructed in the form of atwo-coil rotary setter, as already mentioned, has two windings which areoffset at an angle of 90°. Controlling direct currents are impressed onthe two windings in an independent manner through the three-conductorconnection 9. Thus, depending on the ratio of the magnitudes of thedirect currents, a magnetic field directed in a specific direction canbe produced in the two-coil rotary setter. This field is followed by abipolar permanent-magnet rotor, not illustrated, which is in rigiddriving connection 7 with the choke valve 5. Such a two-coil rotarysetter is a quick-acting final control element in comparison with astepping motor, and through it a direct positioning of the choke valveis effected. The electric drive 6 has no effect on the main throttle andthere is no stepped cone present as some existing devices. The finalcontrol element renders possible a very fine setting for every operatingtemperature and every region of the performance graph of the engine.

Thus, by means of the present invention, cold-starting, running-up,hot-running and transition mixture enrichment is carried out solely byactuation of the choke valve by a single final control element.Electronic control of the mixture composition of air and fuel iseffected in static and in dynamic operation. The electric drive 6 takesover the functions of a bi-metal spring, of an engine inlet vacuumcontrol and of an accelerator pump. This results in a considerablysimpler and more economical construction and more accurate and easieroperation. Consequently, the problems of pollutants in the exhaust gas,the running behaviour and the fuel consumption of the engine isconsiderably improved. The microprocessor makes possible a simpleadaptation of the individual operations to the particular requirements,for example corrections in the idle running range or very great degressof opening of the main throttle in order to avoid a desired deviation inthe mixture composition. Depending on the operating parameters fed intothe microprocessor, these corrections can be carried out solely byinfluencing the electrical input to the microprocessor in which therequired functions can be realised by the cyclic sequence of a pluralityof sub-routines.

Instead of detecting certain other operating parameters, in FIG. 1d, anair volume meter 60 is provided in the air flow path of the mixturegenerator 1 and a line 62 connects the output of the meter 60 to theinput of the control device 8.

We claim:
 1. In a method of operating a combustible mixture generator ofan internal combustion engine to produce a transition mixture enrichmentduring acceleration of said engine, said mixture generator includingmeans defining a mixing chamber, a main throttle downstream of saidchamber, a choke valve upstream of said chamber, an electric drive foroperating said choke valve, means for sensing at least one operatingparameter of said engine, and a control device which is controlled bysaid sensing means and controls said electric drive to move said chokevalve into positions for cold starting, running-up and hot-runningmixture enrichment, said method comprising the steps of holding saidchoke valve open in steady operation of said engine, sensing theinstantaneous degree of opening of said main throttle valve with thesensing means, and when the speed of opening said main throttle exceedsa predetermined threshold value conveying respective signals from thesensing means to the control device and from the control device to theelectric drive for temporarily abruptly at least partly closing saidchoke valve by a predetermined magnitude by means of said electric driveand measuring at least one of a plurality of operating parameters ofsaid engine and making said predetermined magnitude and the duration ofsaid closing of said choke valve dependent upon the measurements of saidat least one parameter.
 2. A method as claimed in claim 1, in which saidoperating parameters include the magnitude of the opening of the saidmain throttle before acceleration starts, the speed of opening of saidthrottle during acceleration, engine temperature and engine speed andfurther comprising using control signals from said sensed parameters,feeding said control signals to an electronic controller and causingsaid electronic controller to control said electric drive.
 3. A methodas claimed in claim 1, further comprising the step of gradually openingsaid choke valve after said temporary abrupt closing of said valve.
 4. Amethod as claimed in claim 3, in which said gradual opening of saidchoke valve is carried out linearly in time.
 5. In a method of operatinga combustible mixture generator of an internal combustion engine toproduce a transition mixture enrichment during acceleration of saidengine, said mixture generator including means defining a mixingchamber, a main throttle downstream of said chamber, a choke valveupstream of said chamber, an electric drive for operating said chokevalve, means for sensing at least one operating parameter of saidengine, and a control device which is controlled by said sensing meansand controls said electric drive to move said choke valve into positionsfor cold starting, running-up and hot-running mixture enrichment, saidmethod comprising the steps of holding said choke valve open in steadyoperation of said engine and temporarily abruptly at least partlyclosing said choke valve by means of said electric drive upon operationof said main throttle to accelerate said engine, measuring a pluralityof operating parameters of said engine and making the magnitude andduration of said closing of said choke valve dependent upon themeasurements of said parameters, said operating parameters include themagnitude of the opening of the said main throttle before accelerationstarts, the speed of opening of said throttle during acceleration,engine temperature and engine speed and further comprising using controlsignals from said sensed parameters, feeding said control signals to anelectronic controller and causing said electronic controller to controlsaid electric drive so that the magnitude and duration of said closingof said choke valve are decreased in relation to the increase of saidopening of said main throttle before acceleration, the decrease of thespeed of opening of said main throttle, the increase of said enginetemperature and the increase of said engine speed.
 6. In apparatus forsupplying combustible fuel mixture to an internal combustion engine,said apparatus providing transition enrichment required duringacceleration of the engine comprising a combustible mixture generator,said mixture generator including means defining a mixing chamber havingan upstream and a downstream end, a main throttle located at thedownstream end of said chamber, a choke valve located at the upstreamend of said chamber, an electric drive connected to said choke valve foropening and closing said choke valve, a control device, meansoperatively connecting said control device to said electric drive, meansfor sensing at least one operating parameter of said engine, and meansoperatively connecting said sensing means to said control device wherebysaid control device causes said electric drive to move said choke valveinto positions for cold starting, running-up and hot-running mixtureenrichment in dependence upon said at least one parameter, theimprovement wherein said electric drive includes a quick-acting rotarydrive motor and means torsionally rigidly connecting said quick-actingdrive motor to said choke valve, said choke valve normally maintained inthe open position during engine operation, and further comprising meansfor sensing the opening of said main throttle above a predeterminedthreshold valve during acceleration operation, said throttle sensingmeans comprising a position sensor coupled to said main throttle valvefor detecting the instantaneous degree of opening of said main throttlevalve and for producing a signal, and means for communicating the signalfrom said sensor to said control device whereby said control devicecauses said electric drive to close said choke valve abruptly andtemporarily by a predetermined amount when opening of said main throttlevalve above the predetermined threshold value is sensed by said throttlesensing means.
 7. Apparatus as claimed in claim 6, in which said mainthrottle comprises a flap and means pivotally mounting said flap. 8.Apparatus as claimed in claim 7, in which said angular-position sensorcomprises a potentiometer, a movable tap on said potentiometer and meansdrivingly mechanically connecting said tap to said throttle. 9.Apparatus as claimed in claim 7, in which said angular-position sensorcomprises an inductive angle indicator and means coupling said indicatorto said main throttle.
 10. Apparatus as claimed in claim 7, in whichsaid angular-position sensor comprises an optical angle indicator andmeans coupling said indicator to said main throttle.
 11. Apparatus asclaimed in claim 6, in which said control device includes a circuitconnected to said sensor for sensing the opening of said main throttle,said circuit differentiating with respect to time said opening of saidmain throttle and providing a signal indicating the rate of opening ofsaid throttle.
 12. Apparatus as claimed in claim 6, further comprisingan engine speed sensor and at least one engine temperature sensor andmeans connecting said engine speed sensor and said at least one enginetemperature sensor to an input of said control device, said engine speedand said engine temperature forming at least some of said operatingparameters of said engine.
 13. Apparatus as claimed in claim 12, inwhich said at least one engine temperature sensor is arranged to sensethe temperature of a wall of an inlet manifold of said engine. 14.Apparatus as claimed in claim 13, in which said sensor for sensing thetemperature of said wall is disposed in the vicinity of an enginecooling water passage of said engine.
 15. Apparatus as claimed in claim6, in which said control device is a microprocessor including a memory,said memory having performance data of said engine stored therein, andsaid microprocessor converting said at least one parameter into controlsignals for controlling said electric drive in dependence upon saidparameters and said data.
 16. Apparatus as claimed in claim 6, furthercomprising means defining an air flow path of said mixture generator andair-volume meter means in said air flow path, said meter means producingoutput signals dependent upon said air volume flowing in said air flowpath and means for feeding said signals to said control device.
 17. Inapparatus for supplying combustible fuel mixture to an internalcombustion engine, said apparatus comprising a combustible mixturegenerator, said mixture generator including means defining a mixingchamber, a main throttle downstream of said chamber, a choke valveupstream of said chamber, an electric drive for opening and closing saidchoke valve, a control device, means operatively connecting said controldevice to said electric drive, means for sensing at least one operatingparameter of said engine, and means operatively connecting said sensingmeans to said control device whereby said control device causes saidelectric drive to move said choke valve into positions for coldstarting, running-up and hot-running mixture enrichment in dependenceupon said at least one parameter, the improvement wherein said electricdrive includes quick-acting drive means and means torsionally rigidlyconnecting said quick-acting drive to said choke valve and furthercomprising means for sensing the opening of said main throttle, saidsensing means producing a signal and means communicating said signal tosaid control device whereby said control device causes said electricdrive to close said choke valve abruptly and temporarily when opening ofsaid main throttle is sensed by said sensing means, said choke valveincludes a choke valve flap and means pivotally mounting said chokevalve flap and said electric drive comprises a two-coil rotary setterincluding a first winding, a second winding offset at an angle of 90° tosaid first winding, means for feeding direct currents independently tosaid first winding and said second winding, a permanent-magnet rotorcontrolled by said windings and means torsionally rigidly connectingsaid rotor to said choke valve flap.